1. Field of the Invention
The present invention relates to a HT-AttPSM (high-transmittance attenuated phase-shift mask) blank, which particularly performs proper transmittance and reflectance at an exposure 193 nm wavelength, and low inspection transmittance at the 257 nm wavelength.
2. Description of the Related Prior Arts
Currently, HT-AttPSM is developed as the focus margin increases with improvement of the photoresist technologies and the chrome assist feature. By employing the HT-AttPSM technique, the ArF lithography may have the potential to reach the 65 nm technology node.
The key optical requirements for an HT-AttPSM blank are: (1) a 180° phase shift, (2) a transmittance between 15˜25%, preferably 18˜20%, and (3) a reflectance less than 15% at an exposure wavelength of 193 nm; and (4) an inspection transmittance less than 40% at a wavelength of 257 nm.
Materials now used for AttPSM at wavelengths of 193 or 248 nm are hard to inspect at the 257 nm wavelength due to their high transmittance, and the reflectance of their coatings at the exposure wavelength is about 12˜20%. However, a three-stacked (Ta2O5)x/(Al2O3)1-x thin film exhibits a reflectance less than 7% as π-phase shifters at 248 nm wavelength, which indicates that composite multilayer films may be good candidate material.
TiO2 and amorphous Al2O3 thin films have been widely used as material for many applications due to good properties such as chemical inertness, mechanical strength, hardness and satisfactory optical characteristics. TiO2 films are generally used in applications such as corrosion protection, wear resistance, electronics and optics. Amorphous Al2O3 thin films are widely used in applications such as in optics, corrosion protection, wear resistance and electronics. However, their application as HT-AttPSM blanks in ArF lithography has not yet been reported.
Therefore, it's desired to develop a novel composite material for HT-AttPSM to solve the above problem.